This invention relates generally to the field of wireless communications and, more particularly, to the field of ring alert terminations in a wireless communication system.
Digital wireless communication systems employ synchronous or asynchronous transmission protocols. Synchronous transmission protocols require rigid timing and structure of transmissions between communication elements. Typically, one communication element will be designated as a node, reference or origin communication element, for example as at least one satellite of a constellation of satellites. Other non-reference communication elements, such as individual subscriber units (ISUs), operating within the communication system must adhere to the timing and frequencies established by the reference communication element.
A reference communication element transmits information, such as ring alert data, in order to attempt to connect a call to an ISU, consistent with the timing and frequency established within the communication system. Ring alert data is normally carried within broadcast channels directed along a beam transmitted by one or more reference communication elements.
A user with an ISU is normally located in an area having a clear line of sight view of the satellite of a constellation of satellites (normally referred to as SV constellation). In this environment, the ISU has about a 90% chance of successfully terminating a call. Typically, each reference communication element uses a series of small spot beams which move across the face of the earth. The use of small spot beams helps increase frequency reuse in the communication system and therefore allows for greater capacity for the limited spectrum available.
Small spot beams also necessitate that ring alert signals be transmitted via several spot beams in order to cover an area that an ISU can be in. In other words, a plurality of broadcast channels located within a predetermined number of spot beams issue a ring alert signal or transmission indicating a pending call.
However, most of the time, an ISU is in standby mode. When an ISU is in standby mode, it normally rescans for the strongest beam for monitoring ring alerts as infrequently as possible (normally every 60 seconds) in order to conserve battery power, because frequent rescans reduce the available standby battery life, and because ring alerts can be lost during the rescan process.
In like manner, an ISU can originally pick a beam which is optimum for receiving a ring alert at the time of the rescan. However, because the reference communication element is normally moving with respect to the earth, and because the ISU can also be moving upon the face of the earth, such as in a car, train, or airplane, this beam will become progressively less optimum as time goes by.
As a result, when an ISU picks a beam to monitor for ring alerts, it might not be the optimum or strongest beam because communication system resources limit the number of beams that can be economically rung at any one given time. Normally, about 4.5 beams are rung per ring alert. However, for battery conservation reasons, the ISU will hang onto a beam for so long that the system has a reasonable chance of not ringing the beam that the ISU is listening to, even when the ISU is placed in an optimum environment.
Therefore, what are needed are a system and a method for enhancing ring alert or call terminations in a communication system where the reference and nonreference communication elements are not stationary. What are also needed are a system and a method for enhancing ring alert or call terminations that maximize system resources and conserve energy.